In situ thermal recovery of oil from an oil shale



Sw 1 1958 D.w. PEACOCK ETAL; 7 3,400,762 I SITU THERMAL RECOVERY OF OILFROM AN OIL SHALE FRACTUR'NG filed July 8 l 6 FRACTURING V PRESSREPRESSURE /L '6' OVERBURDEN 2m FRACTURES PRoPPEo/fl J AM I PRODUCTION ETO CONDENSER PROPPED FRACTURES/7 q Kf q M PYROLYSIS ZONE 'SATURATEDkSTEAM STEAM ZONE PLUS H2O H "FRACIURES on. FLOW THROUGH eobodo ooaooo JINVENTORS PYROLYSIS DUE TO BUgNlgGa DML PEACQCK i v as. NEEDHAM I fATTORNEYS as 42 FIG. 2 Y Y a I l.

3 7 NR PRODUCTION 4o 44 L I ABSTRACT OF THE DISCLOSURE An oil shaleformation penetrated by an injection well and a production well isfractured from one well to the other. A portion of the fracturedformation extending part of the way between the wells is subjected tosuperheated steam, and oil is recovered through the production well. Thesteamed portion of the formation is then subjected to in situ combustionto produce additional oil in the production well. The. steaming and.combustion of steamed portions are alternately continued until thecombustion front reaches the production well.

This invention relates to a process for producing oil from an oil shale.

- Large deposits of oil in the form of oil shale are found in varioussections of the United States and, particularly.

in Colorado and surrounding states. Various methods of recovery'of'oilfrom these shale deposits have been proposed andthe principal ditiicultywith these methods is ihe high cost which renders the recovered oil tooexpen sive to compete with petroleum crudes recovered by moreconventional methods. The in situ retorting of oil shale to recover theoil contained therein is made diificult because of the nonpermeablenature of the oil shale and the difficulty of applying heat theretowithout extensive mining or drilling operations. The mining and removalof the oil shale for retorting of the shale in furnaces outside theformation is commercially uneconomical in most cases.= I I Thisinvention is concerned with a process for the therma! recovery of oilfrom shale in situ which avoids mining and removal of the oil shale forretorting.

Accordingly, it is an object of the invention to provide a process forthe thermal in situ production of oil from an immrmeable oil shale.Another object is to provide a iijiliifiil rates Fatent G Patented Sept.10, 1968 jection steps either by injecting a propping agent into theprocess for'the production of oil from oil shale by in situ I heatingwhich avoids mining of the shale and retorting of same above ground.Other objects of the invention will become apparent to one skilled inthe art upon consideration of the accompanying disclosure.

. A broad aspect of the invention comprises fracturing an oil shale byconventional fracturing techniques between an injection well and aproduction well penetrating the shale stratum, preferably, at severaldifferent levels therein and holding the fracture(s) open; injectingsuperheated steam into the fractures of the stratum thru the injectionwell so as to heat the stratum and establish a thermal front therein;after a substantial sectionof the stratum has been heated and oil driventherefrom thru the fractures into the production well, terminating steaminjection and injecting combustion-supporting, (Il -containing gas intothe stratum (fractures) thru the injection well so as to initiate adirect drive in situ combustion operation thru the section of stratumheated by the steam;

and repeating the stream injection and gas injection steps sequentially,the produced oil and gas from the steam and fractures during or afterthe fracturing operation or by maintaining suflicient gas pressure inthe stratum during the injection steps to hold the fractures open.

In order to efficiently heat the stratum during steam injection, it ispreferred to operate with steam at a temperature of at least 800 F., andmore desirably, 1000 F. The steam injection phase or step of theoperation heats and fluidizes the kerogen or solid oil in the oil shale,rendering the same readily flowable as liquid and vapor. Steam injectionis continued for a period ranging from" several weeks to several monthsso as to heat a substantial section of the oil shale extending in therange of 5 to 25 feet or more into the stratum from the injection welland the oil thermally produced from the shale is driven thru thefractures into the production well from which it is readily produced bypumping or in other conventional manner.

Air is the preferred combustion-supporting gas because of its readyavailability and low cost but oxygen-enriched air may be utilized. Uponcontacting the hot oil shale with air, combustion is initiated whichadds additional.

pyrolysis zone formed during the steam injectionstep,

air injection. is terminated and steam injection isfagain resumed. Afteranother substantial steam injection period, this step is terminated andair is again injected thru the injection well into the expandedpyrolysis zone for further combustion of residual coke and hydrocarbonmaterial therein. The alternate movement of the pyrolysis zone by steamand combustion greatly increases the recovery of shale oil compared toeither method alone and more rapidly opens up the entire shale stratumto gas flow, rendering the stratum more permeable.

A more complete understanding of the invention may be had by referenceto the accompanying schematic draw ing of which FIGURE 1 is an elevationthru a stratum penetrated by an injection well and a production well,illustrating the fracturing and propping phase of the operation; FIGURE2 is a similar view illustratingthe conditions in the stratum after asubstantial steam injection period; and FIGURE 3 is a similar viewillustrating the combustion phase of the operation.

Referring to FIGURE 1, an oil stratum 10 is penetrated by an injectionwell 12 and a production well 14. Tubing string 16 in injection well 12extends to a lower section of stratum l0 and forms an annulus 18 withthe wall of the well or casing 20. A packer 22 packs off the annulus atthe approximate top level of the shale stratum. A similar arrangement inwell 14 includes a tubing 24, a casing 26, and a packer 28. Fracturingfluid is applied thru tubing 16 and tubing 24, if desired, so as tobuild up sufficient fracturing pressure to produce fractures at selectedlevels, such as 30, 32, 34, and 36. If the fracturcs are to be propped,the propping agent in the form of hard, rugged, particulate material isinjected with either the fracturing fluid near the end of the fracturingoperation or after fracturing has been effected. The fracturing andpropping operation is a conventional operation that needs no furtherdiscussion.

Casing strings 20 and 26 may be cemented in at the top of the stratum orthey may extend to the bottom, in which case they are perforated atselected levels therein coinciding with the fracturing levels (and atintermediate levels, if desired). I

Referring lu FHlURH 2, a steam generator 38 provides steam from a sourceof water not shown and the steam passes thru line 40 to a steamsupcrheutcr 42 for healing to the desired temperature. The superheatedsteam is injected thru line linlo tubing 16 from which it passes to thewell below packer 22 tmdcnters fractures 30, 32,

34, and 36, which are either held open by propping material or by steaminjection pressure by regulating the back pressure on well 14. After anextended steam injection period, a saturated steam zone exists betweendotted line 46 and 48 with a steam plus condensate (H O) occupying asubstantial zone between lines 48 and 5t The pyrolysis zone extends fromthe wall of well 12 to line 50 at the end of a substantial steamingperiod. The zone between the wellbore and line 46 contains superheated'steam. The steam injection phase of the operation proit-invades thestratum via the wellbore and the several fractures in the stratum. Up'oncontacting the hot stratum containing the superheated steamadjacentwelllZ, the residual coke and/or shale oil is ignited toestablish a combustion front which moves slowly away from the injectionwell as air injection is continued-Acombustion catalyst may be utilized,if desired.

The combustion phase of the operation not only consumes aportion of thecoke and oil as fuel but also fiuidizes additional kerogen andsemi-solid hydrocarbon material to drive additional shale oil from thestratum,

and it also imparts additional heat to the stratum and expands thepyrolysis zone as illustrated at line 5'4. During the combustion step,the additional produced oil is recovered thru tubing string 24 asbefore. The combustion step and the expansion of the pyrolysis zoneopens up additional stratum for passage of gas (steam, air, and/orcombustion gases), materially increasing the permeability I of thestratum adjacent the fractures. By repeating the steam injection'andcombustion steps, the' stratum is opened up completely between thefractures so that sub-' staniially all of the oil in the shale isproduced and production is continued. until the pyrolysis zone isextended completely to the production well and until further injec: tionof steam and air fails to result in economic produc tion of oil.

' Certain modifications of the invention will become apparent to those,skilledinthe art and the illustrative details disclosed are notto' beconstrued as imposing unnecessary limitations on the invention.

We claim: 1. A process for producmg oil from an oil shale stratumpenetrated by an injection well and a production well,

which comprises the-steps of:- 7

4 (n) fracturing said stratum from one well to the other and holdingresulting fracture) open during the following steps; (b) injectingsuperheated steam at a temperature of at least 800 F. thru saidinjection well into said stratum thru said fractureht) so as to heat asubstantial sec-- tion of said stratum extending from said injectionwell part of the distance to said production'well and produce oi]therefrom thru said fracture(s) and thru said production well;

(c) terminating steam injection of step (b) and injecting acombustion-supporting, -containinggas into said stratum thru saidinjection well so as to initiate and maintain a direct drive in situcombustion front thru the hotresidual hydrocarbon and coke in th sectionof stratum heated in step (b);

(d) recovering thru said production well oil produce in step (c);

(e) when the combustion front of step (c) has been driven thru asubstantial portion of the section of stratum heated in step (b)terminating the injection of said combustion-supporting, o -containinggas;

and

(f) repeating steps (b), (c), (d) and (e) a plurality of times toalternately establish a new steam heated portion of saidstratum-extending an additional portion of the distance between saidinjection well and production well and then establish and maintain an insitu combustion front in said new steam heated portion of said stratumuntil the in situ combustion front has been driven thru asubstantialportionof said new steam heated portion, until the in situ com-- bustionfront reaches completely to said production well. 2. The process ofclaim 1 wherein said stratum is fractured at several different levels instep (a). p

3. The process of claim 1 wherein solid particulate propping agent isinjected into the fracture(s) to hold same open. r

4. The process of claim 1 wherein said fractures are held open duringinjection in steps (b) and (c). by pres: sure of the injected gas. 5.;The process of claim 1 wherein said gas is air..

' References Cited UNITED STATES PATENTS --2,780,449 2/1957 Fisher etal. 166-11 2,813,583 11/1957 Marx an. 166-11 3,149,670 9/l964 Grant166-11 3,221,813 12/1965 -Closrnann et al. 166ll 3,284,281 11/1966Thomas ....-L 166 2 3,342,258 9/1967 Prats 166-ll STEPHEN .l.NovosAnPrimr Examiner.

